Integrated circuits (ICs) are at risk of damage due to electrostatic discharge (ESD) events. ESD events may be caused by an electrostatically charged person holding an IC chip. An ESD event may involve electrostatic potentials of 4000 Volts or more between input/output (I/O) terminals of the IC chip. During the ESD event, a discharge current flows between an I/O terminal and ground through vulnerable circuitry in the IC chip.
ESD protection devices are incorporated into IC chips across two terminals of the IC chip. ESD protection devices are often configured to protect the vulnerable circuitry by providing another path to ground for the discharge current. For example, an ESD protection device may be connected between an I/O terminal and a ground or common terminal. The ESD protection device acts as a voltage limiter to prevent the voltage between the I/O terminal and the ground terminal from reaching levels that would otherwise harm one or more transistor or other devices on the chip.
ESD protection devices are configured to remain quiescent while the voltage between the terminals falls within a normal operating range for the IC chip. When the voltage reaches a triggering voltage above that range, the ESD protection device turns on to shunt any damaging current to ground, thereby preventing damage to the IC chip. The triggering voltage of the ESD protection device should exceed the maximum normal operating voltage of the IC chip to avoid interfering with the normal operation of the IC chip.